Events, K.K. Slider Songs, new homepage section for events + villager birthdays

Features:

• Added 'Events', with detail view
• Added Collectible Songs
• Added a homepage section for current + upcoming events
• Added a homepage section for upcoming villager birthdays
• On your profile, show how many items you're ahead/behind the server
• Menu uses a dropdown button to display more items

Fixes:

1. Menu properly fits on mobile now, with Art disappearing behind the 'Misc' menu item

Dev:

1. Added unit tests